A mass spectrometer (MS) is a device that filters gaseous ions according to their mass-to-charge (m/z) ratio and measures the relative abundance of each ionic species. A typical mass spectrometer comprises an ion source, wherein the ions are generated; a mass filter, wherein the ions are separated in space or in time; an ion detector, wherein the filtered ions are collected and their relative ion abundance measured; a vacuum system; and a power source to power the spectrometer. Depending on the type of sample and the method of introducing the sample into the mass spectrometer, ions can be generated in the ion source by electron impact ionization, photoionization, thermal ionization, chemical ionization, desorption ionization, spray ionization, or other processes.
Mass spectrometers are generally classified according to the basis on which the mass filtering is accomplished using electric and/or magnetic fields. Mass filter types include magnetic-sector, time-of-flight, linear quadrupole, ion cyclotron resonance, and ion traps. Detection of ions is typically accomplished using a single-point ion collector, such as a Faraday cup or an electron multiplier, or using a multipoint collector, such as an array or a microchannel plate collector, whereby all of the ions arrive at the collector simultaneously.
Conventional mass spectrometers use metallic components that are fabricated using standard metal machining techniques. The metallic components cause such mass spectrometers to be large and bulky, which limits the widespread application and deployment of such devices. Further, the metallic components are expensive to manufacture and assemble together. With reference to FIG. 1, shown is a simplified diagram of a quadrupole assembly 2 of rod-shaped electrodes 4. Each electrode 4 is a metallic rod of circular cross-section. The four rods are arranged precisely one relative to another in two electrode pairs aligned with and opposed across the device centerline. An ion volume 6 is defined between the electrodes 4, within which volume the ions are transmitted along the z-direction either with or without mass filtering, depending on the particular voltages that are applied to the electrodes 4.
FIG. 2 shows an assembly 8 including a plurality of segmented electrodes 10. Assembly 8 is similar to the assembly 2, but each electrode 10 comprises a plurality of individual segments 18, which are electrically isolated one from another. Application of appropriate voltages to the individual segments 18 creates a voltage gradient that is directed along the axial direction (z-direction) within the ion volume 12. The axially directed voltage gradient is used to move ions along the length of the assembly 8.
Electrode assemblies 2 and 8 may be used as ion guides for transferring ions between different stages of a mass spectrometer. Of course, in addition to the quadrupole configurations that are shown in FIGS. 1 and 2, ion guides comprising six electrodes (hexapole) or eight electrodes (octapole) are also known. Further, ion guides having stacked-ring electrode geometries have been described previously, such as for instance ion funnels and ring pole ion guides. All of the above-mentioned types of ion guides must be assembled together, requiring precise alignment of the various electrodes and other components. As a person of skill in the art will undoubtedly appreciate, assembling together the separate pieces of an ion guide is a labor intensive and time consuming process. Further, it is necessary to make electrical connections to each of the individual electrodes in the assembled ion guide structures, which is prone to error and results in complex assemblies.
Considerable effort has been devoted to developing miniature mass spectrometers, particularly for use in field applications including forensics, food and environmental analysis, clinical lab analysis, etc. Such applications require analytical instruments that feature high reliability, robustness, high performance and low cost. Of course, it goes without saying that mass spectrometers based on metallic components fabricated using standard metal machining techniques are not well suited to miniaturization. In particular, miniaturization exacerbates the difficulty of machining components using standard metal machining techniques and subsequently assembling together the individual components.
In U.S. Pat. No. 6,967,326, Pai et al. disclose miniature mass spectrometers comprising multi-layer structures deposited on semiconductor or dielectric wafer-substrates, based on microelectronics processing techniques. Pai et al. teach that the multi-layer structures are built up in multiple vapor-deposition or sputtering steps. Sacrificial materials are used to preserve the structures that are formed in previous steps, necessitating a step with a chemical etchant to remove the sacrificial material and create open structures. The process of forming the miniature mass spectrometers therefore involves numerous steps and the use of potentially hazardous chemicals. Further, since the deposition steps produce planar features that are stacked one on top of another, the types of electrode geometries that can be fabricated using the method that is described by Pai et al. is quite limited. For instance, structures that approximate the rod-shaped electrodes of a quadrupole ion guide cannot readily be fabricated using the technique that is disclosed by Pai et al.
Glasmachers et al. (“Transfer Efficiency and Timing Performance Measurements of Multipole Ion Guides and Ion Wave Guides Constructed with Planar Technologies, Poster Presentation No. ThP 063, 59th ASMS Conference on Mass Spectrometry and Allied Topics (2011)) have disclosed multipole ion guides and ion wave-guides that are constructed using standard high precision technologies for printed circuit boards. A quadrupole ion wave-guide with segmented electrodes is described, in which each of the segmented electrodes is fabricated using PCBs with gold plating to define the electrode segments and electrical connections, etc. Unfortunately, all of the electrode segments are defined along one edge of a substrate, which is pre-cut to a desired shape. As such, each segmented electrode must be fabricated separately and then aligned with three other segmented electrodes during assembly of the quadrupole ion wave-guide. The need to precisely align four segmented electrode structures, in the case of a quadrupole device, complicates assembly and is time consuming. Further, the method that is described by Glasmachers et al. is not well suited for fabricating devices with curved ion transport pathways, etc.
It would therefore be beneficial to provide an ion optics component and a method of making ion optics components, which overcome at least some of the above-mentioned disadvantages.